1. Field of the Invention
The invention relates to fiber-optic diffusers for use in the photodynamic therapy or diagnosis of cancer and related conditions in a patient. The invention provides a method and apparatus for controlling the output distribution of a cylindrical fiber-optic diffuser.
2. Description of the Related Art
"Photodynamic Therapy", (PDT) is a well known method of treating tumors and other diseases in humans in which a photosensitizing substance is administered to a patient and allowed to concentrate preferentially in tumor tissue and then light, at an appropriate wavelength, is used to illuminate the tumor tissue. The light activates a chemical reaction with the substance in the tumor tissue and destroys the cancer cells. Reference is made to U.S. Pat. No. 4,889,129 for a discussion of the particulars of one such PDT method and apparatus for practicing the method.
Since the photoactivation of the photosensitizer in tissue through the absorption of light energy is the primary event leading to photodynamic destruction of tissue, it is critical to deliver the light in a targeted manner to the tumor tissue at an optimum "dose" which is matched to the target tissue volume. This is accomplished through the use of fiber optic delivery systems to target the light at appropriate wavelengths to the tumor tissue to be treated. For tubular body areas such as a bronchus or esophagus, it is common to use a fiber optic diffuser which delivers the light in a cylindrical scattering pattern. Thus, for PDT treatment of esophogeal cancer, an optical fiber is required to be equipped with an apparatus at the tip which disperses light propagating along the fiber in a uniform cylindrical pattern with respect to the central axis of the optical fiber.
U.S. Pat. No. 4,660,925 describes a fiber optic cylindrical diffuser which is constructed of an optical fiber with an exposed core at one end, and a scattering medium surrounding the exposed core constructed to produce the desired uniform cylindrical pattern. The exposed core coated with the scattering medium is then inserted into an open-ended tube and the interstices between the scattering medium and the tubes are then filled with additional scattering medium.
U.S. Pat. No. 5,074,632 discloses an improvement on this method of preparing a cylindrical diffuser which includes an optical fiber with an exposed core tip, a thin layer of scattering medium coated on the exposed tip, and a sleeve member enclosing the tip without touching the scattering medium and fixed on the jacket of the fiber. Both of these devices rely on the diffusing coatings which must be manually applied to the fiber at the time of manufacture to convert the forward moving light stream in the fiber optic into a radially emitting cylindrical light stream.
Another approach to producing approximately uniform cylindrical patterns of light has been taken by Quentron optics Pty. Ltd. of Adelaide, Australia discussed in U.S. Pat. No. 4,660,925. The Quentron fibers utilize a fiber optic core which is tapered to a point at its tip, allowing the light to escape at each point along the tapered core. However, the need to taper the core of the optical fiber at its tip is a time consuming and costly procedure.
In using such cylindrical diffusers for photodynamic therapy, it is essential that the light distribution from the fiber optic be as uniform as possible within a volume of tissue containing a tumor, so the light can be delivered at an appropriate and consistent dosage level. The apparatus must be capable of delivering the light for effective treatment without developing "hot spots" or mechanical or optical failures during use. In addition, the device must be capable of providing consistent output reproducibility. Ideally, the device should be easily modified to provide different output distribution profiles for different applications.